This invention relates in general to a transfer apparatus for use for example in an electrostatographic reproduction device, and more particularly to an improved transfer apparatus including a mechanism for periodically resetting registration between a transfer member and a transferable image support.
In typical electrostatographic reproduction devices (copiers or copier/duplicators), pigmented marking particles are attracted to a latent image charge pattern formed on a support to develop a transferable image on the support. The transferable image support is then brought into contact with a receiver member and an electric field applied to transfer the marking particle developed image to the receiver member from the support. After transfer, the receiver member bearing the transferred image is transported away from the support and the image is fixed to the receiver member by heat and/or pressure to form a permanent reproduction thereon.
One mechanism for application of the electric field to effect marking particle image transfer from the transferable image support to the receiver member is to support the receiver member on an electrically biased roller. The roller is located in contact with the transferable image support and rotated such that the peripheral surface of the roller and the support move substantially together in registration through the area of contact (see for example U.S. Pat. No. 4,739,361, issued Apr. 19, 1988, in the names of Roy et al). In this manner the receiver member is held in transfer relation with the support to enable accurate image transfer to take place. Such roller transfer apparatus offer a distinct advantage in that it maintains a positive (physical) control over the receiver member. This positive control is particularly desirable when a receiver member must be recirculated to have multiple marking particle images sequentially transferred thereto, such as in making multi-color or composite reproductions.
While roller transfer apparatus of the above described type are generally effectively utilized in electrostatographic reproduction devices, registration particularly between sequentially transferred marking particle images is sometimes hard to accurately maintain. Particularly, under certain environmental conditions, and due to ordinary engineering tolerance requirements, the peripheral speed of the transfer roller does not match the speed of movement of the transferable image support. This can cause undesirable forces to be built up in the transfer nip, with ultimate misregistration between subsequently transferred marking particle images. Additionally, the transfer roller may be oriented at some angle relative to the plane of the transferable image support. As such, a force may be imparted to the support to cause the support to move in a cross-track direction with respect to the transfer roller.